Arc chamber with multiple cathodes for an ion source

ABSTRACT

An apparatus for extending the useful life of an ion source, comprising an arc chamber containing a plurality of cathodes to be used sequentially and a plurality of repellers to protect cathodes when not in use. The arc chamber includes an arc chamber housing defining a reaction cavity, gas injection openings, a plurality of cathodes, and at least one repeller element. A method for extending the useful life of an ion source includes providing power to a first cathode of an arc chamber in an ion source, operating the first cathode, detecting a failure or degradation in performance of the first cathode, energizing a second cathode, and continuing operation of the arc chamber with the second cathode.

FIELD

The present disclosure generally relates to ion implantation systems.More particularly, the present disclosure relates to arc chambers of ionsources used in ion implantation systems.

BACKGROUND

Ion implantation is a process that alters the physical, chemical, orelectrical properties of a material and is used in a wide range ofcommercial and industrial applications. In general terms, an ionimplanter generates an ion beam, accelerates the ion beam in anelectrical field, and impacts the ion beam into a solid material. Ionimplantation is used extensively in the fabrication of semiconductors,where doped regions such as sources and drains are formed insemiconductor substrates by implanting ion impurities.

One of the components of an ion implanter is the ion source, whichgenerates the ion beam. An ion source forms an ion beam by admitting asmall amount of gas into an arc chamber's reaction cavity, where aheated cathode emits electrons causing ionization of the gas and theformation of a plasma in the reaction cavity. The positively-chargedions are then drawn from the arc chamber using a negatively-chargedanti-cathode positioned near a small opening in the arc chamber throughwhich the ion beam exits.

There are two types of widely-used ion sources: directly heatedcathodes, having a cathode for emitting electrons—usually a single-turnhelical filament—mounted openly in the reaction cavity, and indirectlyheated cathodes, having a cathode heated by electron bombardment from afilament causing thermionic emission of electrons from the cathode intothe reaction cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will be apparent from elements of the figures, which areprovided for illustrative purposes and are not necessarily to scale.

FIG. 1A is a top view of an arc chamber in accordance with someembodiments of the present disclosure with the first cathode in use.

FIG. 1B is a top view of the arc chamber of FIG. 1A, with the secondcathode in use.

FIG. 2A is a top view of an arc chamber in accordance with someembodiments of the present disclosure with the first cathode in use.

FIG. 2B is a top view of the arc chamber of FIG. 2A with the secondcathode in use.

FIG. 3 is a top view of an arc chamber in accordance with someembodiments of the present disclosure with the first cathode in use.

FIG. 4 is a top view of an arc chamber in accordance with someembodiments of the present disclosure with the first cathode in use.

FIG. 5 is a flow diagram of a method in accordance with someembodiments.

FIG. 6 is a top view of an apparatus for extending the useful life of anion source in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

This description of certain exemplary embodiments is intended to be readin connection with the accompanying drawings, which are to be consideredpart of the entire written description. Terms concerning attachments,coupling and the like, such as “connected” and “interconnected,” referto a relationship wherein structures are secured or attached to oneanother either directly or indirectly through intervening structures, aswell as both movable or rigid attachments or relationships, unlessexpressly described otherwise.

Unfortunately, ion source cathodes are prone to malfunction. Commonmodes of failure for an ion source cathode include filament degradationor failure, typically caused by exposing the filament to the corrosiveeffects of the gas and plasma in the reaction cavity, and componentdegradation, where the gas admitted into the arc chamber gradually formsdeposits on the filament and cathode, resulting in cathode performancebelow an acceptable threshold.

The frequent malfunctions of ion source cathodes result in a high rateof repair or replacement. These repairs and ion source cathodereplacements may be time-consuming and costly because an ion implanterworks at vacuum pressures and the vacuum is broken before maintenancemay be performed. In most applications an ion implanter is kept runningcontinuously between failures to maximize throughput. Thus, the frequentmalfunctions of ion source cathodes reduce ion implanter efficiency andproductivity.

The arc chambers illustrated in FIGS. 1A, 1B, 2A, and 2B are examples inaccordance with some embodiments of the present disclosure. As will beknown to one of skill in the art, an arc chamber is disposed within anion source. An ion source forms an ion beam by admitting a small amountof gas into the arc chamber, ionizing the gas with a heated cathode, anddrawing positively-charged ions from the arc chamber using anegatively-charged anti-cathode.

FIG. 1A is a top schematic view of one example of an arc chamber 100 inaccordance with some embodiments of the present disclosure. As will beknown to one of skill in the art, FIG. 1A illustrates some embodimentsof the present disclosure wherein the cathodes mounted in the arcchamber 100 are directly heated, referred to as Bernas-type cathodes.The arc chamber 100 is generally rectangular or cylindrical in shapewith an arc chamber housing 10 forming a reaction cavity 12 and a recess28. The arc chamber housing 10 is perforated by a plurality of gasinjection openings 14, which admit gas to be ionized during operation ofthe arc chamber 100.

A first directly heated cathode 16 is mounted at one end of the arcchamber 100 and disposed within the reaction cavity 12. In one exampleof the present disclosure, the first directly heated cathode 16 is asingle-turn helical filament. The first directly heated cathode 16 iselectrically isolated from the arc chamber housing 10 by a pair ofisolators 18 and connected to a first power supply 30. A second directlyheated cathode 20 is mounted opposite the first directly heated cathode16. The second directly heated cathode is isolated from the arc chamberhousing 10 by a pair of isolators 32 and connected to a second powersupply 34, which can be the same as the first power supply 30 or can bean independent power supply.

A repeller element 36 is formed from repeller 26 mounted to clapboard22. An axial pin or hinge 24 is disposed through the clapboard 22,permitting the repeller element 36 to rotate around the axis of theaxial pin or hinge 24 from a first position across the reaction cavity12 to a second position in a recess of the arc chamber housing 10. Therepeller element 36 is connected to a rotation assembly 118 whichrotates the repeller element 36 from the first position to the secondposition. The rotation assembly 118 can be implemented in conventionalways, such as by using a motor. The repeller 26 and clapboard 22 can beconstructed from any of a variety of materials including but not limitedto tungsten, molybdenum, boron nitride, or ceramic and combinations orcomposites thereof

The embodiment illustrated in FIG. 1A can further include circuitry tomonitor cathode performance, notify an operator of cathode failure ordegradation, and automatically switch between the first directly heatedcathode 16 and the second directly heated cathode 20. A first detector114 monitors electric current through first directly heated cathode 16,using a detection logic configured to detect when first directly heatedcathode 16 has failed or degraded. First detector 114 is connected toand controls a first power supply controller 110, a first cathode alarm116, the rotation assembly 118, and a second power supply controller112. A second detector 122 monitors electric current through seconddirectly heated cathode 20 and is connected to a second cathode alarm124. A manual switch is provided and connected to the rotation assembly118 to permit an operator to manually switch between the first directlyheated cathode 16 and the second directly heated cathode 20.

FIG. 1B is a top view of the same example of an arc chamber 100illustrated in FIG. 1A. In this view, the repeller element 36,comprising the repeller 26 mounted to a clapboard 22, is rotated via theaxial pin 24 and is now disposed within the recess 28. This uncovers thesecond directly heated cathode 20.

The arc chamber 100 illustrated in FIG. 1A is first operated with therepeller element 36, comprising repeller 26 mounted to clapboard 22,positioned to protect second directly heated cathode 20 from ionbombardment and plasma generated by first directly heated cathode 16.First directly heated cathode 16 is energized by first power supply 30and the arc chamber 100 is operated until first directly heated cathode16 fails or the performance of first directly heated cathode 16deteriorates below an acceptable threshold. The operation of arc chamber100 is then switched between the first directly heated cathode 16 andthe second directly heated cathode 20 either automatically or manually.

In automatic mode, first detector 114 detects the failure of firstdirectly heated cathode 16 and discontinues power to first directlyheated cathode 16 via first power supply controller 110. First detector114 activates first cathode alarm 116, which provides a visual or auralnotification to the operator of the failure or degradation of firstdirectly heated cathode 16. First detector 114 orders rotation assembly118 to rotate repeller element 36 via axial pin 24 from a first positionacross the reaction cavity 12 to a second position in a recess of thearc chamber housing 10. This rotation of repeller element 36 exposessecond directly heated cathode 20 and disposes repeller element 36within recess 28. First detector 114 additionally orders second powersupply controller 112 to energize second directly heated cathode 20.Thus second directly heated cathode 20 is exposed to reaction cavity 12and energized, allowing operation of arc chamber 100 to continue.

In manual mode one or more of the actions performed in automatic mode byfirst detector 114 is performed by the operator. For example, once thefirst detector 114 detects the failure of first directly heated cathode16 and activates first cathode alarm 116 the operator is able tomanually rotate repeller element 36 by use of manual switch 120. Manualswitch 120 directs rotation assembly 118 to rotate repeller element 36.Additionally, the operator can replace first detector 114 altogether.The operator would detect the failure or degradation of first directlyheated cathode 16 by monitoring the ion implanter's performance duringuse, elect to switch between first directly heated cathode 16 and seconddirectly heated cathode 20, manually discontinue first power supply 30to first directly heated cathode 16 via a switch or removal of powersupply cables, manually rotate repeller element 36 by use of manualswitch 120, and manually energize second directly heated cathode 20 withsecond power supply 34 via a switch or manual manipulation of powersupply cables. Thus second directly heated cathode 20 is exposed toreaction cavity 12 and energized, allowing operation of arc chamber 100to continue.

Using either automatic or manual mode the second directly heated cathode20 can be deployed without breaking the vacuum, and withoutre-evacuating the chamber.

As will be appreciated by one of skill in the art, the presentdisclosure is not limited to a first directly heated cathode 16 andsecond directly heated cathode 20 as illustrated in FIGS. 1A and 1B.Additional directly heated cathodes can be mounted in the arc chamber100 in a similar manner and can be disposed within the reaction cavity.As desired, additional repeller elements can also be added to protectadditional directly heated cathodes from ion bombardment while otherdirectly heated cathodes are energized.

FIG. 2A is a top view of one example of an arc chamber 100 in accordancewith some embodiments of the present disclosure. FIG. 2A illustratessome embodiments of the present disclosure wherein the cathodes mountedin the arc chamber 100 are indirectly heated cathodes. This embodimentcan be identical to the embodiment shown in FIG. 1A and as describedabove with the exception of the cathode configuration.

In FIG. 2A a first indirectly heated cathode 50 is mounted at one end ofthe arc chamber 100 and disposed within the reaction cavity 12. A firstfilament 52 is disposed within first indirectly heated cathode 50 andconnected to first power supply 54. A second indirectly heated cathode56 is mounted opposite first indirectly heated cathode 50. A secondfilament 58 is disposed within second indirectly heated cathode 56 andconnected to second power supply 60, which can be the same as the firstpower supply 54 or can be an independent power supply.

FIG. 2B is a top view of the arc chamber 100 of FIG. 2A, with therepeller element 36 rotated to a second position exposing the secondindirectly heated cathode 56. The cathode configuration of FIG. 2Bincluding first indirectly heated cathode 50, first filament 52, firstpower supply 54, second indirectly heated cathode 56, second filament58, and second power supply 60, is identical to the cathodeconfiguration depicted in FIG. 2A and described above.

The arc chamber 100 illustrated in FIG. 2A is first operated with therepeller element 36, comprising repeller 26 mounted to clapboard 22,positioned to protect second indirectly heated cathode 56 from ionbombardment and plasma generated by first directly heated cathode 16.First indirectly heated cathode 50 is energized by first power supply 30and the arc chamber 100 is operated until first indirectly heatedcathode 50 fails or the performance of first indirectly heated cathode50 deteriorates below an acceptable threshold. The operation of arcchamber 100 is then switched between the first indirectly heated cathode50 and second indirectly heated cathode 56 either automatically ormanually. The automatic and manual modes of switching between the firstindirectly heated cathode 50 and second indirectly heated cathode 56 canbe identical to the embodiment shown in FIG. 1A and as described abovewith the exception of the cathode configuration.

As will be appreciated by one of ordinary skill in the art, the presentdisclosure is not limited to a first indirectly heated cathode 50 andsecond indirectly heated cathode 56 as illustrated in FIGS. 2A and 2B.Additional indirectly heated cathodes can be mounted in the arc chamber100 in a similar manner and can be disposed within the reaction cavity.If desired, additional repeller elements can also be added to protectadditional indirectly heated cathodes from ion bombardment while otherindirectly heated cathodes are energized.

FIG. 3 is a top schematic view of one example of an arc chamber 300 inaccordance with some embodiments of the present disclosure. As will beknown to one of skill in the art, FIG. 3 illustrates some embodiments ofthe present disclosure wherein the cathodes mounted in arc chamber 300are directly heated, referred to as Bernas-type cathodes.

In this embodiment, an arc chamber housing 302 forms a reaction cavity304 containing four cathodes and four repeller elements. Arc chamberhousing 302 is perforated by a plurality of gas injection openings 306,which admit gas to be ionized during operation of the arc chamber 300.Arc chamber housing 302 further forms first recess 328, second recess338, third recess 348, and fourth recess 318.

A first directly heated cathode 350 is mounted in arc chamber 300 andelectrically isolated from arc chamber housing 302 by a pair ofisolators 352. First directly heated cathode 350 is connected to firstpower supply 354. A first repeller element 326 is formed from a firstrepeller 322 mounted to a first clapboard 320. A first axial pin 324 isdisposed through clapboard 320, permitting repeller element 326 torotate around the axis of the axial pin 324 from a first positioncovering first directly heated cathode 350 to a second position in firstrecess 328. FIG. 3 illustrates the embodiment with first directly heatedcathode 350 in use. First repeller element 326 is disposed within firstrecess 328 while first directly heated cathode 350 is energized.

Three additional directly heated cathodes are shown in FIG. 3. A seconddirectly heated cathode 356 is electrically isolated from arc chamberhousing 302 by a pair of isolators 352 and is connected to second powersupply 358. A third directly heated cathode 360 is electrically isolatedfrom arc chamber housing 302 by a pair of isolators 352 and is connectedto third power supply 362. A fourth directly heated cathode 364 iselectrically isolated from arc chamber housing 302 by a pair ofisolators 352 and is connected to fourth power supply 368. Each powersupply can be shared between any of the plurality of filaments or can beindependent.

Each of these additional directly heated cathodes are protected from ionbombardment by a repeller element 336 comprising a repeller 332 mountedto a clapboard 330. An axial pin 334 is disposed through clapboard 330,permitting repeller element 326 to rotate around the axis of axial pin324. Each repeller element 336 is shown in a first position covering adirectly heated cathode. In this first position repeller element 336protects a directly heated cathode from ion bombardment. When rotatedaround the axis of axial pin 324, each repeller element placed in asecond position disposed within a recess in the arc chamber housing. Inthis second position repeller element 336 uncovers a directly heatedcathode to permit arc chamber operations with this directly heatedcathode energized.

FIG. 4 is a top schematic view of one example of an arc chamber 400 inaccordance with some embodiments of the present disclosure. As will beknown to one of skill in the art, FIG. 4 illustrates some embodiments ofthe present disclosure wherein the cathodes mounted in arc chamber 400are indirectly heated cathodes. This embodiment can be identical to theembodiment shown in FIG. 3 and as described above with the exception ofthe cathode configuration.

In FIG. 4 a first indirectly heated cathode 402 is mounted to the arcchamber housing 302 and disposed within the reaction cavity 304. A firstfilament 404 is disposed within first indirectly heated cathode 402 andconnected to first power supply 406. A second indirectly heated cathode408 is mounted to the arc chamber housing 302 and disposed within thereaction cavity 304. A second filament 410 is disposed within secondindirectly heated cathode 408 and connected to second power supply 412.A third indirectly heated cathode 414 is mounted to the arc chamberhousing 302 and disposed within the reaction cavity 304. A thirdfilament 416 is disposed within third indirectly heated cathode 418 andconnected to third power supply 418. A fourth indirectly heated cathode420 is mounted to the arc chamber housing 302 and disposed within thereaction cavity 304. A fourth filament 422 is disposed within fourthindirectly heated cathode 420 and connected to fourth power supply 424.Each power supply can be shared between any of the plurality offilaments or can be independent.

The present disclosure further provides a method for extending theuseful life of an ion source. FIG. 5 is a flow diagram of one example ofa method in accordance with some embodiments. After process 500 begins,power is provided at block 510 to a first cathode in an arc chamber. Atblock 520 the first cathode is operated, and at block 530 the failure ordegradation in performance of the first cathode is detected. A secondcathode is energized at block 540, and operation of the arch chamber iscontinued at block 550.

FIG. 6 is a top schematic view of a further embodiment. FIG. 6illustrates an apparatus 600 for extending the useful life of an ionsource by providing a plurality of arc chambers. Apparatus 600 comprisesa plurality of arc chambers (denoted 610-A, 610-B, 610-C, and 610-D)mounted to a plate 620. Plate 620 need not be substantially circular asillustrated in FIG. 6 but can take a variety of forms. Each of theplurality of arc chambers (610-A, 610-B, 610-C, and 610-D) is optionallyone of the types of arc chambers described above and illustrated in FIG.1A, 1B, 2A, or 2B.

Plate 620 is rotatably mounted to an ion source via an axle 622. Axle622 is connected to a rotation assembly 624 that is used to rotate axle622 and plate 620. A switch 626 is provided which allows an operator tomanually control rotation of axle 622 and plate 620. By rotating plate620 the operator sequentially positions each of the plurality of arcchambers (610-A, 610-B, 610-C, and 610-D) to be operationally connectedto said ion source. In the embodiment illustrated in FIG. 6, four arcchambers are mounted to plate 620. If each arc chamber is adirectly-heated cathode type arc chamber as illustrated in FIG. 1A anddescribed above, the operator has eight cathodes available for use. Aseach cathode fails or degrades below an acceptable performance thresholdthe operator switches to a second cathode in an arc chamber or rotatesplate 620 to operationally connect a new arc chamber to the ion source.

The arc chamber embodiments described above include several advantages.First, the useful life of an ion source can be greatly extended byproviding a redundant cathode. Since the cathode is prone to malfunctionand failure, adding at least a second cathode can double the useful lifeof the ion source which reduces costs associated with operating an ionimplanter. Second, the ion implanter, which operates at vacuumpressures, does not need to be opened and re-secured (i.e., sealed andevacuated) each time a cathode fails. Instead, when a first cathodefails a second cathode can be deployed and energized to continue ionimplanter operations, which increases the production or throughput ofthe ion implanter by reducing shutdown and maintenance time.

In some embodiments an arc chamber comprises an arc chamber housing, atleast one repeller element, and a plurality of cathodes. The arc chamberhousing defines a reaction cavity and the arc chamber has a plurality ofgas injection openings and a recess in at least one wall. Each repellerelement comprises a repeller mounted to a clapboard, with the repellerelement pivotally mounted to rotate around an axis from a first positionextending across the reaction cavity to a second position in the recessof the arc chamber housing. Each cathode is mounted in the reactioncavity such that a first one of the plurality of cathodes is directlyexposed to the reaction cavity, and a second one of the plurality ofcathodes is covered by the at least one repeller element when the atleast one repeller element is in the first position.

In some embodiments an arc chamber comprises an arc chamber housing, afirst and second cathode, and a first repeller element. The arc chamberhousing defines a reaction cavity including a recess for accepting a thefirst repeller element. The arc chamber has a plurality of gas injectionopenings. The first and second cathode are mounted within the arcchamber opposite each other. The first repeller element comprises arepeller mounted to a clapboard, the clapboard having an axial pin,permitting the repeller element to rotate around the axis of the axialpin from a first position in which the clapboard extends across thereaction cavity to a second position in which the clapboard is withinthe recess of the arc chamber housing, to selectably cover the secondcathode when the first cathode is in use and to selectably uncover thesecond cathode when the second cathode is in use

In some embodiments a method for extending the useful life of an ionsource comprises providing power to a first cathode of an arc chamber inan ion source, operating the first cathode, detecting a failure ordegradation in performance of the first cathode, energizing a secondcathode, and continuing operation of the arc chamber with the secondcathode.

Although examples are illustrated and described herein, embodiments arenevertheless not limited to the details shown, since variousmodifications and structural changes can be made therein by those ofordinary skill within the scope and range of equivalents of the claims.

What is claimed is:
 1. An apparatus for extending the useful life of anion source comprising: an arc chamber housing defining a reactioncavity, the arc chamber having a plurality of gas injection openings anda recess in at least one wall thereof; at least one repeller element,comprising a repeller mounted to a clapboard, said repeller elementpivotally mounted to rotate around an axis from a first positionextending across the reaction cavity to a second position in the recessof the arc chamber housing; and a plurality of cathodes, mounted in thereaction cavity such that a first one of the plurality of cathodes isdirectly exposed to the reaction cavity, and a second one of theplurality of cathodes is covered by the at least one repeller elementwhen the at least one repeller element is in the first position.
 2. Theapparatus of claim 1, further comprising a power supply for providingelectrical power to a selectable one of the plurality of cathodes. 3.The apparatus of claim 1, further comprising a plurality of powersupplies, wherein each of the plurality of cathodes is electricallypowered independently by a respective one of the plurality of powersupplies.
 4. The apparatus of claim 1, further comprising: at least onerotation assembly connected to the at least one repeller element; and atleast one manual switch connected to the at least one rotation assembly.5. The apparatus of claim 4, further comprising: at least one detectorto monitor cathode performance; at least one alarm to notify theoperator of cathode failure or degradation of performance; and at leastone power supply controller.
 6. The apparatus of claim 1 furthercomprising: a plurality of said arc chambers mounted to a plate, saidplate rotatably mounted to an ion source via an axle, such that rotatingsaid plate allows each of the plurality of said arc chambers to besequentially operably connected to said ion source.
 7. The apparatus ofclaim 6 further comprising: a rotation assembly for rotating said plateconnected to said axle; and a switch connected to said rotationassembly.
 8. An apparatus for extending the useful life of an ion sourcecomprising: an arc chamber housing defining a reaction cavity includinga recess for accepting a repeller mounted to a clapboard, the arcchamber having a plurality of gas injection openings; a first cathodewithin the arc chamber; a second cathode, mounted within the arc chamberopposite the first cathode; and a first repeller element, comprising arepeller mounted to a clapboard, the clapboard having an axial pin,permitting said repeller element to rotate around the axis of the axialpin from a first position in which the clapboard extends across thereaction cavity to a second position in which the clapboard is withinthe recess of the arc chamber housing, to selectably cover said secondcathode when said first cathode is in use and to selectably uncover saidsecond cathode when said second cathode is in use.
 9. The apparatus ofclaim 8, further comprising a third cathode and a second repellerelement, comprising a second repeller mounted to a second clapboard, thesecond clapboard having a second axial pin, permitting said secondrepeller element to rotate around the axis of the second axial pin froma first position, in which the second repeller element covers said thirdcathode, to a second position in which the second repeller element isdisposed within a second recess of the arc chamber housing, the secondrepeller element being selectably positionable to cover said thirdcathode when either of said first or second cathodes is in use and touncover said third cathode when said third cathode is in use.
 10. Theapparatus of claim 9, further comprising a fourth cathode and a thirdrepeller element, comprising a third repeller mounted to a thirdclapboard, the third clapboard having a third axial pin, permitting saidthird repeller element to rotate around the axis of the third axial pinfrom a first position, in which the third repeller element covers saidfourth cathode, to a second position in which the third repeller elementis disposed within a third recess of the arc chamber housing, the thirdrepeller element being selectably positionable to cover said fourthcathode when either of said first, second, or third cathodes is in useand to uncover said fourth cathode when said fourth cathode is in use.11. The apparatus of claim 8, further comprising a power supply forproviding electrical power to a selectable one of the plurality ofcathodes.
 12. The apparatus of claim 8, further comprising a pluralityof power supplies, wherein each of the plurality of cathodes iselectrically powered independently by a respective one of the pluralityof power supplies.
 13. The apparatus of claim 8, further comprising: atleast one rotation assembly connected to the at least one repellerelement; and at least one manual switch connected to the at least onerotation assembly.
 14. The apparatus of claim 13, further comprising: atleast one detector to monitor cathode performance; at least one alarm tonotify the operator of cathode failure or degradation of performance;and at least one power supply controller.
 15. The apparatus of claim 8further comprising: a plurality of said arc chambers mounted to a plate,said plate rotatably mounted to an ion source via an axle, such thatrotating said plate allows each of the plurality of said arc chambers tobe sequentially operably connected to said ion source.
 16. The apparatusof claim 15 further comprising: a rotation assembly for rotating saidplate connected to said axle; and a switch connected to said rotationassembly.
 17. A method for extending the useful life of an ion source,comprising the steps of: providing power to a first cathode of an arcchamber in an ion source; operating said first cathode; detecting afailure or degradation in performance of said first cathode; energizinga second cathode upon detection of the failure or degradation inperformance of said first cathode and without breaking vacuum in saidarc chamber; and continuing operation of said arc chamber in said ionsource.
 18. The method of claim 17, further comprising the steps of:upon detection of the failure or degradation in performance of saidfirst cathode, discontinuing power to said first cathode; after thepower is discontinued, rotating a repeller element within the arcchamber, the repeller element comprising a repeller mounted to aclapboard, to expose said second cathode; wherein the energizing of saidsecond cathode occurs after said cathode is exposed by the rotation ofthe repeller element.
 19. The method of claim 17, further comprising:operating said second cathode; detecting a failure or degradation inperformance of said second cathode; discontinuing power to said secondcathode; rotating a repeller element within the arc chamber, therepeller element comprising a repeller mounted to a clapboard, to exposea third cathode; energizing said third cathode; and continuing operationof said arc chamber in said ion source.
 20. The method of claim 19,further comprising: operating said third cathode; detecting a failure ordegradation in performance of said third cathode; discontinuing power tosaid third cathode; rotating a repeller element within the arc chamber,the repeller element comprising a repeller mounted to a clapboard, toexpose a fourth cathode; energizing said fourth cathode; and continuingoperation of said arc chamber in said ion source.